Energy , Finding Kinetic energy and Potential energy of an object

Energy

It is the ability to do work , Man needs the energy to exert effort ( do work) without energy no task can be performed , The unit of measuring energy is the Joule ( J ) which is the same as the unit of measuringwork , Energy has different forms such as Kinetic energy ( K E ) and potential energy ( P E ) .

Kinetic energy ( K E )

Kinetic energy is the energy possessed by the object due to its motion , When work is done to move an object , this work is acquired by the object as kinetic energy , The unit of measuring the kinetic energy is Joule ( J ) and its dimensions are ML²T−2 .

When the kinetic energy of an object is 400 J , It means that the energy possessed by the object due to its motion = 400 J .

Finding the kinetic energy of an object

If a force ( F ) acts on an object of mass ( m ) at rest to move it at a uniform acceleration ( a ) to reach velocity ( vf ) after moving a displacement ( d ) .

On applying the brakes to stop a car moving at velocity30 km/h , the car would slide for a distance ( d ) before stopping .

The same car would slide for a distance four times longer on applying the brakes to stop it , if the car was moving at velocity 60 km/h , F d ∝ v² .

Potential energy ( P E )

It is the energy stored in the objects because of their new positions or state , When an object is lifted up , work is done , This work is stored in the body as energy known as gravitational potential energy , The unit of measuring the potential energy is the Joule ( J ) and its dimensions are ML²T−2 .

When the potential energy of an object is 50 J , It means that the energy stored in the object because of its new position or state = 50 J .

Finding the potential energy of an object

If an object of mass ( m ) is lifted up to a height ( h ) , the work done ( W ) is determined by the relation : W = F . h , Where ( F ) is the force required to lift the object up and equals its weight ( w ) :

Examples of potential energy

Stored energy in a spring when compressed or elongated ( elastic potential energy ) , The spring does work to release this energy and restore its original position .

Stored energy in an object when raised up above the ground ( gravitational potential energy ) , gravitational potential energy depends on the object position relative to the surface of the Earth .

Stored energy in a stretched rubber band ( elastic potential energy ) , The stretched rubber band shrinks when removing the acting force to restore its original shape .

Stored energy in electrons inside a battery ( electric potential ) , Electronsflow when the battery is connected to a closed circuit .

To lift a box of weight450 N vertically to a height of 1 m , We need a force equal to the box weight , The work done : W = 450 N × 1 m = 450 J

When raising the same box using a ramp ( inclined plane ) 3 m long , A force less than its weight is required ( 150 N ) but for a longer displacement , The work done : W = 150 N × 3 m = 450 J .

The sum of Kinetic energy and Potential energy is called Mechanical Energy .

Mechanical Energy = Kinetic energy + Potential energy

ME = KE + PE

Physics for the environment

Most of the energy used by man comes from non-renewable resources such as Coal , Petroleum , Non-renewable resources of energy are considered as unclean resources since they produce a lot of harmful products to the environment and man health .

Because of this , there is a global trend , especially in the most industrialized countries , to used the renewable resources such as wind power and waterfalls as an energy resource to generate electricityand preserve the environment , as well .